It is desired to prevent or to reduce as much as possible leakage of fluid through a valve inserted in the fluid pipeline system. This is particularly desired where the service fluid is either toxic or lethal and in many other applications where it is desired to increase the time periods between maintenance shutdowns to correct any leakage problems occurring in the system.
Fluid valves presently in use for instance use one or more packing rings axially mounted around the fluid valve stem and in frictional engagement therewith. Positive loading means have been attempted to apply a positive load on the packing members to keep the valve stem centered in the packing in an attempt to prevent the leakage of fluid along the valve stem.
For instance, packing ring members formed of tetrafluorethylene (TFE) material are in common use. TFE has a temperature coefficient of expansion which is about 10 times that of metal. In a normal operation of a fluid valve and within its normal intended environment, the packing material tends to expand and contract due to temperature cycling and due to the valve movements. Coil springs are currently in use to apply a positive or live load to the packing material. In some packing configurations, Belleville spring washers are placed around each packing stud in an attempt to apply uniform concentric loading of the Bellevilles onto the packing members, usually through a packing follower. A uniform loading is difficult to achieve in this configuration because it depends upon an equal tightening of the packing studs around the valve stem.
Another attempt to apply a uniform load to the valve stem packing has been to use a coil spring concentrically mounted around the valve stem to apply a load to the packing member. Typically, the inner diameter of the coil spring is purposely made larger than the valve stem diameter to prevent the coil spring from hanging up on the valve stem during its operation. However this spacial separation between the coil spring and the valve stem can permit the spring to apply undesired side loading on the packing members and thereby causing movement of the packing ring members away from the valve stem thereby leading to the leakage of fluid through the valve. Such leakage is of course highly undesired where the service fluid is either toxic or lethal and therefore this leads to maintenance shutdowns in order to remedy the problem. Undesired side loading in such coil spring configurations also may be caused by the unevenness of the formed ends of the coil spring causing uneven loading contact with the packing.
Accordingly, it is desired to provide an improved live load packing system which can apply a uniform load to the valve stem packing and maintain such a uniform packing load during valve stroking and thermal service temperature cycling. It is also desired to provide a compact live load packing system to reduce the physical valve size. It is also desired to provide a live load packing system in which there is presented a visual indication when the packing member compression is optimum. This assures that a uniform load to the valve stem packing has been achieved.